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Most of the research we have about sleep has been biased against women. Disappointing? Yes. Surprising? No.
We’ve been told research done on only men could apply to both men and women, but more recent sleep research has shown this assumption may be untrue — let’s talk about it.
Why women may need more sleep than men
There is currently no research proving women have a biological need to sleep more than men. Research does show, however, that women spend more time sleeping than men (11 more minutes on average), but that sleep is reportedly of worse quality. Women are also more likely to have insomnia and develop anxiety disorders, which are largely associated with lower sleep quality, suggesting a physical need for more sleep.
We also have evidence that women’s circadian rhythms differ from men’s — specifically that women have “slightly earlier circadian timing than men,” according to Dr. Renske Lok, a postdoctoral fellow at Stanford University conducting research in sex-based differences in sleep. Dr. Lok recently published a narrative review in Sleep Medicine Reviews that parsed through the academic literature regarding the differences between the way men and women sleep.
Current guidelines say adults between 18 and 64 need between seven to nine hours of sleep per night, according to the National Sleep Foundation. To reach this goal, they recommend trying to go to sleep at the same time every night, avoiding caffeine before bedtime, and keeping your room cooler.
But findings like Dr. Lok’s suggest we may need to update these guidelines to account for gender differences. Let’s break down her main findings and the implications they might have.
Sex differences in circadian rhythms
So, women have slightly earlier circadian timing than men — but what does this actually mean?
Your body has a biological clock that controls your innate sense of time. This biological clock controls your circadian rhythm which, among other functions, tells your body when to get sleepy by releasing melatonin. Your circadian rhythm also dictates when you get hungry, your body’s temperature, and female reproductive hormones.
The review found that women typically release melatonin earlier than men, reach their lowest core body temperature (which signals your body beginning to wake up) earlier than men, and that women enter REM sleep earlier than men but spend eight fewer minutes in it. All of these things correspond with their findings that women have slightly shorter and earlier intrinsic circadian periods. “In practical terms, this often results in women being earlier chronotypes — they prefer to go to bed and wake up earlier compared to men of the same age,” says Dr. Lok.
Some researchers also speculate that these shorter circadian periods can help explain why more women have insomnia, but more research is needed to confirm this link.
So, women might want to go to bed earlier — why does it matter?
If you’ve ever been jet lagged, you understand how even a short-term disturbance in your circadian rhythm can affect you. Sleep disorders are associated with increased occurrence of mood disorders, and research has also shown that disrupted circadian rhythms from shift work, jet lag, and even daylight saving time changes are associated with menstrual cycle disturbances and infertility.
There’s a plethora of scientific evidence that links sleep deficiency and sleep disorders to the development of disease in almost every single human tissue, according to the National Center on Sleep Disorders Research. Sleep is arguably one of the most important biological functions — an undisrupted circadian rhythm is crucial for the healthy regulation of so many important bodily processes, including, for women, their reproductive cycle. This review confirmed not only that there are differences in how men and women sleep, but also that these differences remain severely under-researched thanks to a long history of excluding women and their cycles from research.
Frustratingly, the authors say multiple times that even in many of the studies they reviewed, the original researchers neglected to include whether or not the women were menstruating. “Women may, at times, benefit from more sleep, particularly during certain phases of the menstrual cycle, when physiological demands may temporarily increase sleep need,” Dr. Lok says.
It’s honestly difficult to say currently what these observations mean, but this small amount of progress is grounds to know that recognizing sex-based differences in sleep is necessary for optimizing sleep medicine.
While current research doesn’t definitively say women need more sleep than men, “this doesn’t rule out the possibility,” Dr. Lok explains. “Women should know that their sleep experiences may be influenced by biological and hormonal factors that have not been adequately studied, and that more inclusive, targeted research is urgently needed to close these gaps.”
Eliza Mattson is a journalism student at Northwestern University and a Rescripted editorial intern. She is primarily interested in health and science writing, but she also studies history and economics. When she’s not writing or studying, you can find her rewatching Speed for the millionth time or baking cookies.